Physiological, biochemical and transcriptional analysis reveals the response mechanism of Panax quinquefolius to the stressors of drought and waterlogging

Panax quinquefolius (American ginseng), a perennial plant cultivated extensively across the globe, exhibits diverse pharmacological properties and holds notable economic significance. Water stress can potentially impact the accumulation of ginsenosides, which are the primary pharmacological component of P. quinquefolium. In this study, the morphological, physiological, and biochemical responses of two-year-old seedlings of P. quinquefolius cultivar “LYS1” under different soil relative water contents (RWCs) of 30%, 50%, 70%, and 100% for 21 days were characterized. Additionally, the transcriptional responses to 30%, 70%, and 100% RWC were analyzed at 7 and 21 days. The results showed that both drought (30% and 50% RWC) and waterlogging (100% RWC) stress had a significant detrimental effect on root biomass and root activity, while simultaneously enhancing efficacy of the antioxidant protection system, which suggested that 70% RWC is optimal for the cultivation of P. quinquefolius. Drought stress induced – but waterlogging stress reduced – ginsenoside accumulation in P. quinquefolius root. In particular, drought stress changed the distribution of monomer saponins Rd, Re, Rb1, Rb2, and Rb3, while waterlogging stress altered the distribution of Rd, Re, and Rc. Drought and waterlogging specifically regulated genes involved in several pathways underlying stress tolerance, including phenylpropanoid biosynthesis, signal pathways and ginsenoside biosynthesis in roots. The integration of physiological, biochemical, and transcriptomic evidence resulted in a selection of candidate genes with potential for enhancing stress tolerance in P. quinquefolius. Meanwhile, some candidate genes were found to play potential roles in ginsenoside biosynthesis, including several CYP450s and UDP-dependent glycosyltransferase genes as well as AP2/ERF, bHLH, NAC, MYB, and WRKY transcription factor members. These findings may provide theoretical references for effectively implementing cultivation strategies by regulating soil water conditions and give valuable insights for further investigation into ginsenoside biosynthesis in P. quinquefolius.